The Prime Minister has announced that face masks will be mandatory in an effort to curb the spread of a new Covid variant in the UK.

Boris Johnson addressed the nation during a briefing at Downing Street on Saturday night, November 27, where he confirmed that “temporary and precautionary” measures would be enforced from next week.

It comes after two cases of the Omicron coronavirus variant were identified in England following genomic sequencing.

Go here for the latest coronavirus updates and breaking Covid-19 news

The two cases, which are believed to be connected, were found in Nottingham and Essex, and are linked to travel to southern Africa.

Boris Johnson has warned that the new variant could reduce the effectiveness of vaccines, as he announced a series of measures to tackle the spread of the virus.

This is when the rule on masks will come into force and what you need to know about the other measures:

When will masks be mandatory again?

Health Secretary Sajid Javid has said mandatory mask-wearing will return to shops and public transport on Tuesday.

Mr Javid said the “face-mask rules are planned to come in on Tuesday” to bring the nation back closer into line with Scotland, Wales and Northern Ireland.

Will we have to socially distance and return to working from home?

The Health Secretary confirmed on Sunday that it was “nowhere near” time to reintroduce social distancing rules and work-from-home guidance, despite the raft of precautionary measures being reintroduced to tackle the concerning strain of Covid-19.

“We know now those types of measures do carry a very heavy price, both economically, socially, in terms of non-Covid health outcomes such as impact on mental health,” he told Sky.

“So, if one was to make decisions like that they would have to be done very, very carefully and we’re not there yet, we’re nowhere near that.”

What are the new rules on travel?

Passengers arriving in the UK have been told that from Tuesday morning they will have to take a PCR test for Covid-19, with the expectation they will have to self-isolate until they test negative.

All contacts with a suspected case of Omicron will have to isolate for 10 days, regardless of their vaccination status, amid concerns that existing jabs will be less effective against the strain, which is believed to spread rapidly.

Mr Javid said the testing regime for international arrivals will be introduced “as soon as possible”, despite online passenger locator forms stating PCR tests will be required rather than lateral flow tests from 4am on Tuesday.

Scotland, Wales and Northern Ireland said they intend to mirror the border restrictions.

What has been said about Christmas?

The Health Secretary told families to plan for Christmas “as normal” despite the new rules.

He said it “would be irresponsible to make guarantees” during the ever-changing pandemic, but told Sky’s Trevor Phillips on Sunday: “I think people should continue with their plans as normal for Christmas, I think it’s going to be a great Christmas.”

Meanwhile, Boris Johnson said he is “confident” this Christmas “will be considerably better than last Christmas” during the Downing Street briefing.

When will the rules be reviewed?

Mr Johnson said the measures will be reviewed in three weeks as he warned Omicron appears to spread “very rapidly”, can transmit between the double-vaccinated and may partially reduce the protection of existing vaccines.

He stopped short of announcing his Plan B to tackle Covid-19 this winter, which includes mandatory use of vaccine certificates in certain venues and reinstating work-from-home guidance.

Government advisers on Sage said during a meeting on October 14 that home working is likely to have the greatest individual impact on transmission out of the measures in Plan B, which they said would have the greatest impact if introduced in unison.

What is the latest on Covid vaccines and boosters?

Mr Javid said he expects to receive new advice “imminently”, within the next couple of days, from the Joint Committee on Vaccination and Immunisation (JCVI) after it was tasked with reviewing whether boosters should be extended to all over-18s.

The group will also consider whether second doses should be offered to 12 to 15-year-olds, and whether the waiting time before a booster jab could be reduced.

“I’ve also asked the NHS to prepare for much greater capacity in our vaccination programme,” Mr Javid told The Andrew Marr Show on the BBC.

Professor Anthony Harnden, the JCVI’s deputy chairman, told BBC Radio 4’s Broadcasting House that extending the age range for boosters and reducing the delay before receiving them was “a sensible strategy” and told under-40s to expect third jabs to be offered to them “earlier than we had previously envisaged”.

Have other countries reported cases of the Covid variant?

The UK, Germany and Italy all confirmed the presence of Omicron on Saturday after the variant first detected in South Africa was reported to be in Belgium a day earlier.

How effective will vaccines be on the variant?

Experts hope existing vaccines will still be good at reducing serious disease from Omicron, but manufacturers are looking at tweaks to make them more specific to the variant.

For the latest local news in your area direct to your inbox every day, go here to sign up to our free newsletter